In an inkjet printer, it is necessary to improve a movement speed of nozzle heads or increase the number of the nozzles in order to increase a printing speed, namely, the number of pixels to be printed per a unit time. However, since there is a limit in improvement of the movement speed and increase of the number of the nozzles, there is generally adopted a configuration of increasing the number of the nozzles as a whole by arranging and locating a plurality of nozzle heads in a sub-scanning direction (in a column direction of locating the nozzles) (see Patent Literature 1 and Patent Literature 2).
Generally, in an inkjet printer, an interlace system is adopted to obtain a resolution that is higher than the pitch of the nozzles and to cancel the unevenness referred to as a banding due to variations of the nozzles and an error of a transportation pitch.
The interlace system is, for example, a system in which the movement amount of the ink-jet head in the sub-scanning direction every one main scanning is set to 1/N of the interval of the nozzles arranged in column in the sub-scanning direction of the nozzle heads in the ink-jet head and a specified region is overprinted by main-scanning N times and is printed by forming dots with the ink without a gap.
In the printing by this interlace system, whereas the ink is discharged onto a print material having no ink stuck in the first main scanning of the nozzle heads, the ink is discharged onto the print material having an ink partially stuck in the previous main scanning after the second main scanning. Therefore, there was a problem that the unevenness is produced due to such as a stain of the ink on an image to be formed by an influence of the ink previously stuck on the print material.
For addressing such a problem, there has been suggested a dot recording device in which an ink discharge position in each main scanning and a feed amount of the sub-scanning are set such that the positions of ink drops recorded in the main scanning are not adjacent in arbitrary twice of the main scanning (see Patent Literature 3).
[Patent Literature 1] Japanese Unexamined Patent Publication No. 2007-69428A
[Patent Literature 2] Japanese Unexamined Patent Publication No. 2003-211644A
[Patent Literature 3] Japanese Unexamined Patent Publication No. 2000-185396A